librrd(3)                            rrdtool                           librrd(3)

NAME
     librrd - RRD library functions

DESCRIPTION
     librrd  contains  most  of  the functionality in RRDtool.  The command line
     utilities and language bindings are often just  wrappers  around  the  code
     contained in librrd.

     This manual page documents the librrd API.

     NOTE:  This document is a work in progress, and should be considered incom‐
     plete as long as this warning persists.  For more information about the li‐
     brrd functions, always consult the source code.

CORE FUNCTIONS
     rrd_dump_cb_r(char *filename, int opt_header, rrd_output_callback_t cb,
     void *user)
         In some situations it is necessary to  get  the  output  of  "rrd_dump"
         without  writing  it to a file or the standard output. In such cases an
         application can ask rrd_dump_cb_r to call a user-defined function  each
         time  there is output to be stored somewhere. This can be used, to e.g.
         directly feed an XML parser with the dumped output or transfer the  re‐
         sulting string in memory.

         The  arguments for rrd_dump_cb_r are the same as for rrd_dump_opt_r ex‐
         cept that the output filename parameter is replaced by the user-defined
         callback function and an additional parameter for the callback function
         that is passed untouched, i.e. to store information about the  callback
         state needed for the user-defined callback to function properly.

         Recent  versions  of rrd_dump_opt_r internally use this callback mecha‐
         nism to write their output to the file provided by the user.

             size_t rrd_dump_opt_cb_fileout(
                 const void *data,
                 size_t len,
                 void *user)
             {
                 return fwrite(data, 1, len, (FILE *)user);
             }

         The associated call for rrd_dump_cb_r looks like

             res = rrd_dump_cb_r(filename, opt_header,
                 rrd_dump_opt_cb_fileout, (void *)out_file);

         where    the    last    parameter    specifies    the    file    handle
         rrd_dump_opt_cb_fileout  should write to. There's no specific condition
         for the callback to detect when it is called for the  first  time,  nor
         for  the  last time. If you require this for initialization and cleanup
         you should do those tasks before and after  calling  rrd_dump_cb_r  re‐
         spectively.

     rrd_fetch_cb_register(rrd_fetch_cb_t c)
         If  your  data does not reside in rrd files, but you would like to draw
         charts using the rrd_graph  functionality,  you  can  supply  your  own
         rrd_fetch  function  and  register  it  using the rrd_fetch_cb_register
         function.

         The argument signature and api must be the same of the  callback  func‐
         tion and must be equivalent to the one of rrd_fetch_fn in rrd_fetch.c.

         To  activate  the  callback  function  you  can use the pseudo filename
         cb//free_form_text.

         Note that rrdtool graph will not ask the same rrd for  data  twice.  It
         determines  this  by  building  a key out of the values supplied to the
         fetch function. If the values are the same, the previous answer will be
         used.

UTILITY FUNCTIONS
     rrd_random()
         Generates random numbers just like random().  This further ensures that
         the random number generator is seeded exactly once per process.

     rrd_strtodbl
         an rrd aware string to double converter  which  sets  rrd_error  in  if
         there  is a problem and uses the return code exclusively for conversion
         status reporting.

     rrd_strtod
         works like normal strtod, but it  is  locale  independent  (and  thread
         safe)

     rrd_snprintf
         works   like  normal  snprintf but it is locale independent (and thread
         safe)

     rrd_add_ptr(void ***dest, size_t *dest_size, void *src)
         Dynamically resize the array pointed to by "dest".   "dest_size"  is  a
         pointer  to the current size of "dest".  Upon successful realloc(), the
         "dest_size" is incremented by 1 and the "src" pointer is stored at  the
         end of the new "dest".  Returns 1 on success, 0 on failure.

             type **arr = NULL;
             type *elem = "whatever";
             size_t arr_size = 0;
             if (!rrd_add_ptr(&arr, &arr_size, elem))
                 handle_failure();

     rrd_add_ptr_chunk(void ***dest, size_t *dest_size, void *src, size_t *al‐
     loc, size_t chunk)
         Like  "rrd_add_ptr",  except  the destination is allocated in chunks of
         "chunk".  "alloc" points to the number of  entries  allocated,  whereas
         "dest_size"  points  to the number of valid pointers.  If more pointers
         are needed, "chunk" pointers are allocated and "alloc" is increased ac‐
         cordingly.  "alloc" must be >= "dest_size".

         This method improves performance on hosts with expensive realloc().

     rrd_add_strdup(char ***dest, size_t *dest_size, char *src)
         Like "rrd_add_ptr", except adds a "strdup" of the source string.

             char **arr = NULL;
             size_t arr_size = NULL;
             char *str  = "example text";
             if (!rrd_add_strdup(&arr, &arr_size, str))
                 handle_failure();

     rrd_add_strdup_chunk(char ***dest, size_t *dest_size, char *src, size_t
     *alloc, size_t chunk)
         Like "rrd_add_strdup", except the destination is allocated in chunks of
         "chunk".  "alloc" points to the number of  entries  allocated,  whereas
         "dest_size"  points  to the number of valid pointers.  If more pointers
         are needed, "chunk" pointers are allocated and "alloc" is increased ac‐
         cordingly.  "alloc" must be >= "dest_size".

     rrd_free_ptrs(void ***src, size_t *cnt)
         Free   an   array   of   pointers   allocated   by   "rrd_add_ptr"   or
         "rrd_add_strdup".  Also frees the array pointer itself.  On return, the
         source pointer will be NULL and the count will be zero.

             /* created as above */
             rrd_free_ptrs(&arr, &arr_size);
             /* here, arr == NULL && arr_size == 0 */

     rrd_mkdir_p(const char *pathname, mode_t mode)
         Create  the  directory named "pathname" including all of its parent di‐
         rectories (similar to "mkdir -p" on the command line - see mkdir(1) for
         more information). The argument "mode"  specifies  the  permissions  to
         use. It is modified by the process's "umask". See mkdir(2) for more de‐
         tails.

         The function returns 0 on success, a negative value else. In case of an
         error,  "errno" is set accordingly. Aside from the errors documented in
         mkdir(2), the function may fail with the following errors:

         EINVAL
             "pathname" is "NULL" or the empty string.

         ENOMEM
             Insufficient memory was available.

         any error returned by stat(2)

         In contrast to mkdir(2), the function does not fail if  "pathname"  al‐
         ready exists and is a directory.

     rrd_scaled_duration (const char * token, unsigned long divisor, unsigned
     long * valuep)
         Parse a token in a context where it contains a count (of seconds or PDP
         instances),  or  a  duration that can be converted to a count by repre‐
         senting the duration in seconds and dividing by  some  scaling  factor.
         For  example,  if a user would natively express a 3 day archive of sam‐
         ples collected every 2 minutes, the sample interval can be  represented
         by "2m" instead of 120, and the archive duration by "3d" (to be divided
         by  120)  instead  of  2160  (3*24*60*60  / 120).  See more examples in
         "STEP, HEARTBEAT, and Rows As Durations" in rrdcreate.

         "token" must be a number with an optional single-character  suffix  en‐
         coding the scaling factor:

         "s" indicates seconds

         "m" indicates minutes.  The value is multiplied by 60.

         "h" indicates hours.  The value is multiplied by 3600 (or "60m").

         "d" indicates days.  The value is multiplied by 86400 (or "24h").

         "w" indicates weeks.  The value is multiplied by 604800 (or "7d").

         "M" indicates  months.   The value is multiplied by 2678400 (or "31d").
             (Note this factor accommodates the maximum  number  of  days  in  a
             month.)

         "y" indicates  years.  The value is multiplied by 31622400 (or "366d").
             (Note this factor accommodates leap years.)

         "divisor" is a positive value representing the duration in  seconds  of
         an interval that the desired result counts.

         "valuep"  is a pointer to where the decoded value will be stored if the
         conversion is successful.

         The initial characters of "token" must be the base-10 representation of
         a positive integer, or the conversion fails.

         If the remainder "token" is empty (no suffix), it is  a  count  and  no
         scaling is performed.

         If  "token"  has  one of the suffixes above, the count is multiplied to
         convert it to a duration in seconds.  The resulting number  of  seconds
         is  divided  by "divisor" to produce a count of intervals each of dura‐
         tion "divisor" seconds.  If division would produce a  remainder  (e.g.,
         "5m" (300 seconds) divided by "90s"), the conversion is invalid.

         If "token" has unrecognized trailing characters the conversion fails.

         The  function  returns  a null pointer if the conversion was successful
         and "valuep" has been updated to the scaled value.  On failure, it  re‐
         turns a text diagnostic suitable for use in user error messages.

CLIENT FUNCTIONS
     The following functions are used to connected to an rrdcached instance, ei‐
     ther  via  a unix or inet address, and create, update, or gather statistics
     about a specified RRD database file.

     There are two different interfaces: The rrd_client_ family of functions op‐
     erate on a user-provided client object (rrd_client_t) and support  multiple
     concurrent  connections  to rrdcache instances. The simpler rrdc_ family of
     functions handles connections transparently but can only be  used  for  one
     connection at a time.

     All  of  the  following  functions  and  data  types  are  specified in the
     "rrd_client.h" header file.

     rrd_client_new(const char *daemon_addr)
         Create a new client connection object. If  specified,  connect  to  the
         daemon at "daemon_addr". The connection can later be changed by calling
         rrd_client_connect.

     rrd_client_destroy(rrd_client_t *client)
         Close a client connection and destroy the object by freeing all dynami‐
         cally  allocated  memory.  After calling this function, "client" can no
         longer be used.

     rrd_client_connect(rrd_client_t *client, const char *daemon_addr)
     rrdc_connect(const char *daemon_addr)
         Connect to a running rrdcached instance, specified  via  "daemon_addr".
         Any  previous connection will be closed. If "daemon_addr" is "NULL", it
         defaults to the value of the  "ENV_RRDCACHED_ADDRESS"  environment  ad‐
         dress.

     rrd_client_is_connected(rrd_client_t *client)
         Return a boolean int if the client is connected to the server.

     rrd_client_address(rrd_client_t *client)
         Returns the server address belonging to the current connection.

     rrdc_is_connected(const char *daemon_addr)
         Return  a  boolean  int  to determine if the client is connected to the
         rrdcache daemon specified by the "daemon_addr" parameter.

     rrd_client_ping(rrd_client_t *client)
     rrdc_ping
         Check the client connection by pinging the remote side.

     rrdc_is_any_connected
         Return a boolean int if any daemon connections are connected.

     rrd_client_disconnect(rrd_client_t *client)
     rrdc_disconnect
         Disconnect gracefully from the present daemon connection.

     rrd_client_update(rrd_client_t *client, const char *filename, int val‐
     ues_num, const char * const *values)
     rrdc_update(const char *filename, int values_num, const char * const *val‐
     ues)
         Update the RRD "filename" via the rrdcached. Where "values_num" is  the
         number of values to update and "values" are the new values to add.

     rrd_client_info(rrd_client_t *client, const char *filename)
     rrdc_info(const char *filename)
         Grab  rrd  info  of the RRD "filename" from the connected cache daemon.
         This function returns an rrd_info_t structure of the following format:

             typedef struct rrd_blob_t {
                 unsigned long size; /* size of the blob */
                 unsigned char *ptr; /* pointer */
             } rrd_blob_t;

             typedef enum rrd_info_type { RD_I_VAL = 0,
                 RD_I_CNT,
                 RD_I_STR,
                 RD_I_INT,
                 RD_I_BLO
             } rrd_info_type_t;

             typedef union rrd_infoval {
                 unsigned long u_cnt;
                 rrd_value_t u_val;
                 char     *u_str;
                 int       u_int;
                 rrd_blob_t u_blo;
             } rrd_infoval_t;

             typedef struct rrd_info_t {
                 char     *key;
                 rrd_info_type_t type;
                 rrd_infoval_t value;
                 struct rrd_info_t *next;
             } rrd_info_t;

     rrd_client_last(rrd_client_t *client, const char *filename)
     rrdc_last(const char *filename)
         Grab the unix epoch of the last time RRD "filename" was updated.

     rrd_client_first(rrd_client_t *client, const char *filename, int rraindex)
     rrdc_first(const char *filename, int rraindex)
         Get the first value of the first sample of the RRD "filename",  of  the
         "rraindex"  RRA (Round Robin Archive) index number.  The RRA index num‐
         ber can be determined by pulling the rrd_info_t off the RRD.

     rrd_client_create(rrd_client_t *client, const char *filename, unsigned long
     pdp_step, time_t last_up, int no_overwrite, int argc, const char **argv)
     rrdc_create(const char *filename, unsigned long pdp_step, time_t last_up,
     int no_overwrite, int argc, const char **argv)
         Create RRD database of path "filename".  The RRD will have a step  size
         of  "pfp_step", the unix epoch timestamp to start collecting data from.
         The number of data sources and RRAs "argc" and the definitions  of  the
         data sources and RRAs "argv". Lastly whether or not to overwrite an ex‐
         isting RRD if one is found with the same filename; "no_overwrite".

     rrdc_create_r2(rrd_client_t *client, const char *filename, unsigned long
     pdp_step, time_t last_up, int no_overwrite, const char **sources, const
     char *template, int argc, const char **argv)
     rrdc_create_r2(const char *filename, unsigned long pdp_step, time_t
     last_up, int no_overwrite, const char **sources, const char *template, int
     argc, const char **argv)
         Create an RRD database in the daemon. rrdc_create_r2 has the same para‐
         meters as rrdc_create with two added parameters of; "sources" and "tem‐
         plate".

         where  "template"  is  the  file path to a RRD file template, with, the
         form defined in rrdcreate(1),

         The "sources" parameter defines series of file paths with data defined,
         to prefill the RRD with. See rrdcreate(1) for more details.

     rrd_client_flush(rrd_client_t *client, const char *filename)
     rrdc_flush(const char *filename)
         flush the currently RRD cached in the daemon specified via "filename".

     rrd_client_forget(rrd_client_t *client, const char *filename)
     rrdc_forget(const char *filename)
         Drop the cached data for the RRD file specified via "filename".

     rrdc_flush_if_daemon(const char *daemon_addr, const char *filename)
         Flush the specified RRD given by "filename" only if  the  daemon  "dae‐
         mon_addr" is up and connected.

     rrd_client_fetch(rrd_client_t *client, const char *filename, const char
     *cf, time_t *ret_start, time_t *ret_end, unsigned long *ret_step, unsigned
     long *ret_ds_num, char ***ret_ds_names, rrd_value_t **ret_data)
     rrdc_fetch(const char *filename, const char *cf, time_t *ret_start, time_t
     *ret_end, unsigned long *ret_step, unsigned long *ret_ds_num, char
     ***ret_ds_names, rrd_value_t **ret_data)
         Perform a fetch operation on the specified RRD Database given be "file‐
         name",  where  "cf"  is  the consolidation function, "ret_start" is the
         start time given by unix epoch, "ret_end" is the endtime. "ret_step" is
         the step size in seconds, "ret_ds_num" the number of  data  sources  in
         the RRD, "ret_ds_names" the names of the data sources, and a pointer to
         an rrd_value_t object to shlep the data.

     rrdc_stats_get(rrd_client_t *client, rrdc_stats_t **ret_stats)
     rrdc_stats_get(rrdc_stats_t **ret_stats)
         Get stats from the connected daemon, via a linked list of the following
         structure:

             struct rrdc_stats_s {
                 const char *name;
                 uint16_t type;
                 #define RRDC_STATS_TYPE_GAUGE   0x0001
                 #define RRDC_STATS_TYPE_COUNTER 0x0002
                 uint16_t flags;
                 union {
                     uint64_t counter;
                     double   gauge;
                 } value;
                 struct rrdc_stats_s *next;
             };
             typedef struct rrdc_stats_s rrdc_stats_t;

     rrdc_stats_free(rrdc_stats_t *ret_stats)
         Free the stats struct allocated via rrdc_stats_get.

   SEE ALSO
     rrcached(1)  rrdfetch(1)  rrdinfo(1)  rrdlast(1)  rrdcreate(1) rrdupdate(1)
     rrdlast(1)

AUTHOR
     RRD Contributors <rrd-developers@lists.oetiker.ch>

1.11.0                             2026-08-08                          librrd(3)
